1. Field of the Invention
This invention relates to braking systems for railcars. More particularly, the present invention relates to an improved braking system for a lightweight railcar moving vehicle comprising a modified semi-tractor wherein the braking system of the connected railcar(s) is connected to and actuated by the compressed air braking system of the semi-tractor.
2. State of the Art
In the railroad industry, maintenance of way is a critical activity and a major expense. Frequently, when maintenance is needed at a particular location along the right-of-way and heavy equipment or materials are required, a work train and crew are sent to that location to perform the needed repairs. For example, a work train may carry a load of railroad ties and short sections of rail for repairing track, along with heavy equipment for unloading and installing these items. Often, a work train consists of a locomotive pulling a single work car, and the maintenance work can be performed by one or two workers.
However, this approach can be very cost inefficient. Because maintenance of way crews and locomotive crews are differently trained and unable to perform each other's duties, the work train will frequently employ a crew much larger than actually needed at any given time. Obviously, this is costly. Furthermore, the use of a typical locomotive--which may cost in excess of a million dollars--to transport a single car and a few workers is extremely cost inefficient. For these reasons, it would be desirable to have a railcar moving vehicle that can pull one or a few railcars along the railroad track at mainline speeds, but that is not a conventional locomotive, and thus is not as costly as a locomotive, nor requires a full locomotive crew. With such a vehicle, a work crew could transport themselves to the work site with their materials and equipment, and perform the work with far less expense.
Additionally, it would be desirable to have such a railcar moving vehicle that is operable both on rails and on roadways. Such a vehicle would be valuable for maintenance of way crews by allowing a work crew to transport themselves and their equipment by highway to a rail siding, where the crew simply transfers their materials and equipment to a waiting railcar, and uses the semi-tractor on the rails to pull the railcar to the work site.
This sort of vehicle would have additional uses, as well. For example, many railroad customers have a need to move railcars and highway trailers within a rail yard or industrial siding. However, except for the largest industries, the cost to purchase and maintain a conventional switching locomotive is prohibitive or economically unwarranted. Thus, lightweight, multipurpose railcar moving vehicles have been developed and used to perform many functions normally assigned to switching locomotives, but which may also be used off the track to move trailers and containers about a switching yard or industrial site. Such modified or hybrid vehicles are more economical for many industries because of their relatively low cost and high versatility. They allow smaller industries to take advantage of the efficiency and economy of rail transport for heavy freight where otherwise they would not be able to do so.
However, conventional railcar moving vehicles are still relatively highly specialized, limited production vehicles. The cost per horsepower of these vehicles is significantly higher than the cost of a conventional semi-tractor, for example, which enjoys the cost advantages of much greater mass production. Additionally, conventional railcar moving vehicles are not designed or configured to operate on public highways as long or short haul trucks, but are confined to the industrial site or switching yard. Many of them do not have the functional and safety equipment required to be street legal, and are designed for low speed operation only, being unable to travel at speeds beyond 15 to 20 miles per hour. Moreover, they cannot operate at top speed for extended periods of time without overheating their hydraulic systems. To address these problems, railcar moving vehicles which are constructed from mass produced vehicles such as semi-tractors have been devised to reduce the acquisition cost and versatility of these vehicles.
Normally, the brakes of railroad cars are linked through a common line to the locomotive, which provides pressurized air to operate the braking system of all attached railroad cars. However, when a lightweight railcar moving vehicle such as a modified semi-tractor is coupled to a standard railcar, braking is a major concern. Because a single loaded railcar may weigh many times more than the lightweight railcar moving vehicle, the lightweight vehicle will be able to provide only a small fraction of the braking force needed for stopping in a reasonable distance, especially in an emergency. Obviously, it is desirable to utilize the railroad car brakes in order to take advantage of the weight of the railcar in braking. Conventional railcar moving vehicles known in the art do this by providing a compressed air link to the brake pipe of the connected railcar, thus using the railcar's braking system to stop.
A schematic diagram of a conventional railroad car braking system is given in FIG. 1, which depicts a string of conventional railcars 10 having steel wheels 12 riding on steel rails 14, and coupled together by couplers 16. Each railroad car 10 has installed thereon a brake pipe 18, piston valve 20, reservoir 22, and brake cylinder 24. The brake pipe 18 is in fluid communication with the piston valve 20 through valve 26 which can be opened or closed to allow or prevent compressed air in the brake pipe 18 to pass. Under normal conditions, and as shown in FIG. 1, valve 26 is open. Two conduits 28 and 30 connect the piston valve 20 to the reservoir 22, and one similar conduit 32 connects the piston valve 20 to the brake cylinder 24. The brake cylinder 24 comprises an actuating rod 34 which extends from the cylinder and is axially reciprocally moveable depending on the pressure in the brake cylinder 24. This actuating rod 34 is connected via a mechanical linkage 35 (not shown in its entirety) to the individual brake actuators 36 on each wheel 12 of the railcar in a manner well known in the art.
The brake pipe 18 is connected to the brake pipes 18 of both preceding and following railcars 10, by flexible hoses 38. It will be appreciated that any railcar 10 may be connected to a locomotive and the brake pipe of the locomotive, rather than another railcar, in the same manner.
The typical railcar braking system thus shown operates in the following manner. The locomotive provides compressed air to the brake pipe 18 which communicates along the entire length of the train. Railcar braking systems typically maintain a running pressure of 90 psi in the brake pipe and associated components. With valve 26 open, this operating pressure is maintained within piston valve 20, conduit 28, and reservoir 22. In a non-braking condition, the pressure in conduit 32 is less than that in the brake pipe and other components mentioned, and is approximately equal to atmospheric pressure.
To actuate the brakes of the railcar, the locomotive engineer moves a brake actuating lever (not shown) which opens a valve to allow pressure to escape from the bake pipe 18. Because the brake pipes of all connected railcars are in fluid communication, this action simultaneously releases the pressure in the brake pipes of all connected railcars. When pressure is released from the brake pipe 18, the change in pressure actuates the piston valve 20 to close off its connection to the brake pipe, and simultaneously release compressed air from the cylinder 22, through conduit 30, thence into conduit 32 and the brake cylinder 24. This actuation thus prevents compressed air from reservoir 22 from escaping through the brake pipe, but sends it instead to the brake cylinder 24. Pressurization of brake cylinder 24 in turn causes actuating rod 34 to extend, thus mechanically actuating the brakes 36 of the railcar.
To release the brakes, the system must regain its operating pressure. This requires that the engineer move the brake lever back to the position which will close the release valve, so that the compressor on the locomotive may repressurize the system. Repressurization requires that pressure be built up in all components of all railcars--the brake pipe 18, piston valve 20, and reservoir 22. As pressure in the brake pipe increases, the piston valve 20 changes position such that reservoir 22 is repressurized, and the pressure in the brake cylinder 24 is simultaneously released.
The design of this braking system provides a "failsafe" design because while the brake cylinders operate by means of pressurized air, the system which powers these cylinders is actuated by the release of pressure, not the maintenance of pressure. Thus, a leak anywhere in the system (except in an individual brake cylinder) will automatically cause the brakes to be applied on the entire train. For example, if two connected railcars become uncoupled, the connecting hoses 38 will pull apart, causing the pressure in the brake pipe 18 to be released. This rapid pressure drop will cause the full pressure of the reservoir 22 of each railcar to immediately actuate the brakes on each railcar. It will be apparent that the actuating pressure of the brake cylinder 24 will be something less than the operating pressure maintained in the cylinder 22 because of the need to pressurize a larger volume (both the reservoir 22 and the brake cylinder 24) using the compressed air in the reservoir 22.
However, conventional railroad car braking systems suffer from several problems in their normal operating mode, which adversely affect operation when connected to a lightweight railcar moving vehicle, especially for maintenance work. First, due to the "failsafe" design, it is rather slow to react. Brake actuation is a two step process, requiring the release of pressure from the brake pipe common to all connected railcars before the brake cylinders begin to actuate. This can involve a substantial volume of air, which takes time to release through the single release valve in the locomotive. Additionally, because of this slow reaction time, a train that has just braked to a stop cannot quickly release its brakes and resume movement again. Obviously, this slow braking system reaction time will slow down the work of a maintenance crew.
Moreover, frequent stopping and starting is problematic with conventional railcar braking systems. Each time the brakes are applied, some portion of the compressed air in the system is released. If the brakes are applied several times in close succession, enough of the pressure in the brake reservoirs can be bled away that the brakes become inoperable until the system regains its operating pressure. This can take a substantial amount of time, potentially leaving a moving train without brakes, and possibly creating a "runaway" train. This is a particular nuisance when using a lightweight railcar moving vehicle for maintenance of way operations where very brief stops are required at locations very close together, such as to throw rail switches, or to set out or pick up railroad ties or other track material.
Semi-tractors normally include compressed air systems for powering the brakes of a standard highway trailer. However, these are actuated by means of providing high pressure air, not by releasing it. Accordingly, it is apparent that the respective braking systems of the train and semi-tractor operate in directly opposite manners. Nevertheless, it would be desirable to have a braking system for a lightweight railcar moving vehicle constructed from a conventional semi-tractor, wherein the compressed air system for providing braking power to a highway trailer is adapted to power the braking system of a railroad car, and the braking system for the railcar may be actuated by the same means that actuates the highway trailer brakes on conventional semi-tractor trailer combinations. It would also be desirable for a lightweight railcar moving vehicle to have a braking system that uses the brakes of the railcar, but does not rely on the slow reaction time of the railcar braking system.